Falling into Pure Pressure... or Not?

Mallory is 16 years old, a sophomore in high school, at her first real party. She was uncomfortable with the idea of going and sneaking out of her house, but her friends reassured her that it was okay and they would take care of her. Mallory is the more shy member of her friend group, but everyone at school thinks she is super nice and she is well liked amongst her peers. They made a pact they would not let her get into a bad situation that she did not feel comfortable in, and if she wanted to leave they would all leave with her.

What do you think she should do first?